This invention relates to a composition of polyoxyalkylene polymers and more particularly to polyoxyalkylene compositions as mold release agents or lubricants in molding processes.
In the molding of natural and synthetic rubber and certain other polymers, generally an efficient mold release agent or lubricant is required to overcome the tendency of the polymer to stick to the mold which is often of metal. Both high temperatures and high molding pressures are often encountered in such molding processes. To facilitate the removal of the molded objects, lubricants of the prior art have generally included mineral waxes, vegetable waxes, fatty acids, and metallic soaps which are applied by spray or other methods of coating to the mold surface.
It is also known to use polyoxyalkylene compounds such as block and heteric copolymers of ethylene oxide and propylene oxide for this purpose. An important application is for use as a lubricant in the production of tires and rubber hose. In the latter case it is used as a lubricant to allow easy removal of radiator-type hose from the mandrels used to form the hose during vulcanization. A preferred material for such application is generally referred to as EPDM.
The term "EPDM" is used in the sense of its definition as found in ASTM-D-1418-64 and is intended to mean a terpolymer of ethylene, propylene and a diene monomer. Illustrative methods for preparing such terpolymers are found in U.S. Pat. No. 3,280,082 and British Patent No. 1,030,289, the disclosures of which are incorporated herein by reference. The preferred terpolymers contain from about 40 to about 80 weight percent ethylene and from about 1 to about 10 weight percent of the diene with the balance of the terpolymer being propylene. This is an elastomer which can be vulcanized; used for automotive parts, cable coating, hose, footwear, and other products.
The copolymers employed in the prior art as mold release agents present problems in that they do not give complete wetting on the EPDM elastomer surface and tend to solidify and flake off after vulcanization, thus giving a non-uniform appearance which is found objectionable by customers for these products. It is desirable for such products to give good wetting both before and after vulcanization. Also, the rubber products should have a matte finish, i.e., be free from shine or at least from a high shine and the mold release composition should give complete wetting both at room temperature and 45.degree. C.
U.S. patent application Ser. No. 675,018 now U.S. Pat. No. 4,555,549 discloses an improved mold release agent with excellent properties, particularly with respect to the above problems, that is to say it gives complete wetting both before and after vulcanization and leaves a matte finish. While the copolymers employed in this application are excellent mold release agents, they do present some problems with respect to warm weather storage of the rubber parts in that the mold release agent tends to ooze out of hoses during warm weather storage.
U.S. Pat. No. 3,504,081 discloses lubricants useful as parting agents in molded rubber articles. These comprise a mixture which includes monoalkylphenyl ethers of lower molecular weight polyethylene glycols wherein the alkyl group may be a straight or branched chain group from about 8 to 12 carbon atoms and a polyethylene glycol containing from about 4 to about 6 ethyleneoxy units. A second component is a higher molecular weight ethylene glycol.
U.S. Pat. No. 4,217,394 discloses mold release compositions suitable for lubricating metal molds employing polyoxyalkylene compounds and including mixtures of more than one polyoxyalkylene compound.